Sealing mechanism for strapping machines



United States Patent John R. Beach Elmhurst, Ill.

Dec. 4, 1967 Dec. 29, 1970 Signode Corporation Chicago, III.

a corporation of Delaware lnventor Appl. No. Filed v Patented Assignee SEALING MECHANISM FOR STRAPPING MACHINES i,

452; 8l/9.l, 9.1H, 9.1M, 9.1 1, 301; 140/932, 93.4

Primary Examiner-Charles W. Lanham Assistant ExaminerE. M. Combs Attarney-Edwai'd R. Lowndes ABSTRACT: A ram-actuated, opposed jaw type seal-crimping mechanism for strapping machines employing a special toggle linkage foroperating the crimping jaws and by means of which a shorter ram stroke than has heretofore been used is made possible. A pin'and-slot connection between the spreader links of the toggle joint and the jaw members reduces the overall toggle link spread necessary to close the seal-crimping aws.

PATENTEUDECZQHU 3.550647 saw 1 [1F 3 INVENTOR JOHN R, BEACH PATENTEUUEUZSIEB I 3,550,647

sum 3 OF 3 IN VE/VTOR JOHN R. BEA CH SEALING MECHANISM FOR STPING MAC The present invention relates to package binding tools commonly referred to as strapping tools, and by means of which a loop of flexible metal strapping which has been caused to encircle an article, or series of articles, is tensioned and thereafter a seal which has been positioned about the overlapping end regions of the loop is crimped or otherwise defonned to provide a seal joint, after which the feed end region of the strapping is severed to free the tensioned loop and the article encircled thereby from the source of strapping. More specifically, the invention is concerned with a novelsealing mechanism which is useable in connection with such strapping tools and by means of which a pair of composite jaws are caused to close upon a prepositioned seal, which is held thereby, for the purpose of crimping such seal about the overlapping portions of the strapping. A sealing mechanism of this general type is shown and described in US. Pat. to Ericsson et al., No. 3,198,218, granted on Aug. 3, 1965 and entitled Strapping Tool, and the present invention is designed as an improvement over such sealing mechanism.

The sealing mechanism of the present invention has been designed for use primarily in connection with portable pneumatically operable heavy duty strapping tools of the general type illustrated in'the above-mentioned patent. The invention may, however, find utility in the metal-strapping field, as for example in connection with large automatic package handling equipment, or with small manually operable strapping tools. Therefore the exemplary portable tool subsequently described represents only one environmental disclosure with which the present sealing mechanism may be associated, it being distinctly understood that a wide variety of other environments are contemplated. Irrespective however of the particular use to which the present invention may be put, the essential features thereof remain substantially the same.

The exemplary tool which embodies the improved sealing mechanism involves in its general organization a base, a frame secured to the base, a gripper for holding the free end of the strap, tensioning means for moving the overlapped portion of the strap relative to the free end, a motor for operating the tensioning means, a magazine for holding a stack of metal seals, opposed coacting composite jaws for applying a seal around the edges of the overlapped portions of the strap and crimping the same, an ejector finger for feeding the metal seals individually and successively to the jaws, a piston-actuated ram for operating the jaws, a cutter blade for shearing the upper overlapped strap portion, and a valve mechanism for operating the tensioning motor and piston-actuated ram. Since the present invention is concerned only with the sealing mechanism of the tool, i.e. the coacting jaws and the actuating means therefor, such sealing mechanism has been illustrated and described in detail herein, the remainder of the tool being shown somewhat schematically and only in sufficient detail to render its environmental function clear.

ln order to facilitate a clear understanding of the improvements which have been embodied in the present invention, it is deemed necessary to set forth in some detail the nature and mode of operation of the conventional-sealing mechanism which is exemplified by the aforementioned US. Pat. No. 3,198,218, similar mechanisms being employed in connection with a wide variety of strapping tools and machines. Such conventional mechanisms employ a toggle linkage consisting of a pair of upper spreader links which have their upper or proximal ends pivotally connected to a vertically movable pistonactuated ram, and having their lower or distal ends pivotally connected to the upper ends of respective jaw members. The jaw members are pivoted medially of their ends for swinging movement in unison and in opposite directions, the lower ends of such members constituting jaws proper which move toward each other for seal crimping purposes under the influence of the spreader links as the ram descends during the power stroke of the piston. As the jaws move inwardly toward each other, an initial wrapping of the seal about the overlapping portion of the strapping takes place, this operation entailing little or no pressure of the seal upon the strapping. Continued inward movement of the jaws results in a terminal application of high pressure to the strapping along the edge regions thereof as these edge regions become compressed between the seal flanges and the crown portion of the seal. Where relatively wide steel strapping is concerned the jaws are usually of a composite sectional nature and reaction anvil members, commonly referred to as notcher blocks, are interposed between adjacent jaw sections and rest against the crown portion of the seal while the intervening jaw sections force the steel laminae consisting of increments of the seal flanges, the edges of the steel strapping, and overlaying increments of the seal crown upwardly between adjacent notcher blocks so as to displace a series of two or more spaced-apart offset tabs or ears out of the general plane of the flattened seal, thereby positively interlocking the overlapping portions of the strapping so that there can be no slippage. Such notching" of the seal and its contained strapping invariably requires a high terminal application of pressure to the seal by the opposed crimping jaws.

Sealing mechanisms of the type briefly outlined above are possessed of certain limitations, a principal limitation residing in the fixed correlation between the movement of the ram and the swinging seal crimping jaws proper. Because the toggle linkage mechanism involved embodies fixed pivot points between each pair of adjacent links, each increment of jaw closing movement is necessarily accompanied by a corresponding increment of ram movement. Thus, the ram is obliged to travel downwardly an appreciable distance during its power stroke in order to effect wrapping of the seal about the strapping, and to travel an additional distance in order to eflect the terminal or final seal notching operation, full power being applied to the ram-actuating piston during its entire power stroke. As a consequence, not only is a relatively long power stroke required, thus necessitating a fairly massive piston and cylinder arrangement, but additionally large quantities of air are consumed in operating the tool. Furthermore, such an arrangement involves the use of relatively long links in the linkage system, thus further contributing toward overall massive tool design.

The present invention is designed to overcome the above noted limitation that is attendant upon conventional sealing mechanism for strapping tools and, toward this end, the invention contemplates the provision of a novel-sealing mechanism wherein, by means of a sliding connection between each of certain pairs of adjacent toggle links, the overall throw of the seal-engaging jaws, i.e. the extent of their inward jaw-closing movements, remains the same as heretofore, while an appreciably shorter ram stroke is required, thus, in the case of pneumatically operated tools, enabling a reduction in the length of the effective piston movement required to move the jaws and a consequent reduction in the height of the piston chamber or cylinder. Reduced cylinder height results in a corresponding reduction in overall tool height, as well as in a reduction in weight. The use of shorter toggle links similarly contributes toward compactness of tool design.

In the case of small manually operated tools, appreciably less effort is required to effect a sealing operation inasmuch as the relatively light ram pressure required to produce the wrapping action of the seal flanges about the strapping is attained during a short initial movement of the operating lever of the sealing mechanism as distinguished from the relatively long lever stroke formerly required to produce such wrapping operation. Furthermore, according to the present invention, the aforementioned lost motion connection which exists between certain pairs of adjacent toggle links results in the application of a camming action by the spreader links against the jaw members during the initial wrapping portion of the seal crimping cycle, this camming action replacing a large portion of the formerly required wide toggle spread. Then, after such camming action has effected the wrapping of the seal flanges about the strapping, a true toggle action is initiated whereby, utilizing only a small toggle spread, the final seal-notching operation is effected, all in a manner that will be described in detail presently. As will be more readily apparent when the nature of the invention is better understood, the relatively long and lightly opposed stroke of the operating lever formerly required to produce a slow wrapping action is, according to the present invention, replaced by a relative short stroke producing a rapid wrapping action which is opposed by an appreciably greater reaction force. Such increased reaction force is however well within the capabilities of the operator and it has the tendency to distribute the reaction to operating lever movement uniformly over the entire stroke of the lever, the latter encountering substantially the same resistance to its movement during the wrapping portion of the crimping cycle as during the notching cycle. A relatively short lever movement, unaccompanied by jerking movements is therefore attainable due to a more uniform ram effort curve." In the case of power-actuated tools, the absence of a sudden increase of reaction force to continued downward movement of the ram and its associated piston results in a smoother and more silent operation of the tool during the crimping cycle.

The provision of a sealing mechanism for strapping tools such as has briefly been set forth above and possessing the stated advantages constitutes the principal object of the present invention. Numerous other objects and advantages, not at this time enumerated, will readily suggest themselves as the following description ensues.

In the accompanying three sheets of drawings forming a part of this specification, one illustrative embodiment of the invention has been shown.

In these drawings:

FIG. 1 is a side elevational view of a pneumatic-strapping tool embodying the improved-sealing mechanism of the present invention;

FIG. 2 is a bottom plan view of the structure shown in FIG. 1;

FIG. 3 is a sectional view taken substantially on the line 3-3 of FIG. I and showing the seal-crimping jaws in their fully retracted position and at a point in the operating cycle immediately following the feeding of a seal thereto;

FIG. 4 is a fragmentary sectional view similar to FIG. 3 showing the seal-crimping jaws in the position which they assume after the wrapping portion of the tool cycle has been completed and immediately prior to the notching operation;

FIG. 5 is a sectional view similar to FIG. 4, showing the crimping jaws in their final closed position after the notching operation has been completed;

FIG. 6 is a fragmentary exploded perspective view of a ram release mechanism employed in connection with the invention; and

FIG. 7 is a fragmentary sectional view taken substantially on the line 7-7 of FIG. 2.

Referring now to the drawings in detail and in particular to FIGS. 1 and 2, an exemplary form of pneumatic-strapping tool embodying the improved-sealing mechanism of the present invention has been designated in its entirety at 10. This strapping tool is of the general type shown and described in the aforementioned US. Fat. to Ericsson et al., No. 3,198,218 and only such portions of the tool as contribute toward and understanding of a suitable environment for the present sealing'mechanism have been illustrated herein, these portions being only briefly described. For a full understanding of the nature and operation of the illustrated tool 10, reference may be had to such patent.

Briefly, the tool 10 involves in its general organization a base frame or foot assembly 12 to which a handle 14 is secured,'the latter extending upwardly and rearwardly from the front end of the foot assembly and terminating in a suspension loop 16 which overlies the center of gravity of the tool and by means of which the tool as a whole may be suspended from an overhead adjustable convenience cable (not shown). The base 12 is provided with a flat bottom surface 18 adapted to be supported on the article 19 undergoing strapping and it is formed with a pair of spaced wings 20 and 22 which project laterally from one side of the base and provide a gap or void 24 therebetween which is sufficiently long as to permit entry of the jaws associated with the sealing mechanism of the present invention for the purpose of crimping a metal seal such as has been shown at S in FIG. 3 around the overlapped portions of a flat metal strap 25 and thereby securing the seal in position on the strap so that it assumes the condition in which it is shown in FIG. 5.

The sealing mechanism, which will be described in detail presently, has been designated in its entirety at 30 and the stacked seals S are fed thereto from a magazine 32 by means of an ejector arm 34 which engages the lowermost seal in the stack and pushes the same between the opposed seal-crimping jaws associated with the sealing mechanism 30, all in a manner that will be made clear presently. Both the ejector arm 34 and seal magazine 32 are supported on a main frame or casting, various portions of which appear in FIGS. 1 and 2 and which have been severally designated at 36. The frame is secured by cap screws 38 to the foot assembly 12. The main frame 36 also serves to support a combined valve and cylinder housing 40 which provides a cylinder section '42 and a valve section 44. The cylinder section 42 bears a direct relation to the present sealing mechanism 30, this relation being set forth in detail subsequently. The valve section 44 however is only indirectly related to the sealing mechanism and therefore the details thereof have not been illustrated. It is deemed sufficient for purposes of disclosure herein to state that the valve mechanism is effective under the control of a pair of levers 46 and 48 to perform certain control functions, among which are initiating the strap tensioning operation and initiating the strap-sealing and shearing operation.

At the front of the base frame 12, an integral support 50 projects upwardly and carries a transverse rock shaft 52 to which there is secured a tiltable frame 53 on which there is mounted a'pneumatically operable tensioning motor'54. A feed wheel 56; carried on a shaft 58 cooperates in the'usual manner of feed wheel operation with a toothed anvil or backup pad 60 on the base frame 12 which grips the-lower overlapping portion of the strap and holds the same fixed while the feed wheel impels the upper portion of the strap in a strap-tensioning direction. The shaft 58 is carried on the frame 53 at a region below the level of the rock shaft 52 so that when rocking movements are imparted to the frame about the axis of the rock shaft 52 thefeed wheel 56 may be raised and lowered out of and into cooperation with the backup pad 60' while at the same time the tensioning motor will be moved between a lowered and a raised position. Releasable latchmeans (not shown) is provided for maintaining the tiltable frame 53 in its inoperative position wherein the feed wheel 56 is raised from the strapping while a spring encircles the rock shaft 52 and yieldingly biases the frame 53 toward its operative position of feed wheel engagement with the strapping. At the rear end of the tool a depressible spring biased lever 62 controls the raising and lowering movements of a rear-toothed gripper element 64, the latter serving to anchor the free end of the strap at the time of initial loading of the tool.

After the sealing mechanism 30 has been operated to effect crimping of the seal S about the overlapping portions of the tensioned loop of strapping, a cutter blade 66 which is carried? by a movable sealing unit proper 70 and which moves bodily; therewith, is caused to descend against a fixed cutter block 72 I to effect shearing of the free end portion of the strapping to thus free the tensioned loop of strapping so that the strapped article may be removed from the strapping tool.

The arrangement of parts thus far described are purely conventional and no claim is made herein to any novelty associated with the same, the novelty of the present invention residing rather in the construction and operation of the sealing mechanism 30 which will be described now in detail.

Referring now additionally to FIGS. 3, 4 and 5. the sealing mechanism 30 of the present invention is operable under the control of a vertically movable ram associated with the cylinder section 42 of the housing 40 and which is provided with a stern portion 102 and an enlarged head portion 104.

The stem portion 102 is fixedly secured to a piston 106 which is disposed within a cylinder proper 108 embodied in the section 42 of the housing 40. The stem portion 102 of the ram 100 projects through the bottom wall 110 of the cylinder, the head portion 104 being disposed externally of the cylinder 108 and being slidable in a vertical bore 112 provided in a jaw support 114. The lower end of the ram is bifurcated as indicated at 116 and a transverse thrust pin 118 projects across the furcations thereof and serves as the motivating thrust member for actuating an articulated toggle linkage assembly 119 the nature of which will be set forth presently.

The jaw support 114 is formed with a depending side plate 120 (see also FIGS. 1 and 7) which, in combination with the aforementioned cutter blade 66, establishes a cagelike enclosure 122 for the jaw linkage assembly 119. The cutter blade 66 is secured to the jaw support 114 by means of an integral square lug or pilot boss 124 (FIG. 7) which projects into a square opening 126 in the cutter blade and which serves to maintain the cutter blade and its attached jaw support 114 in an erect condition and to guide the same in their vertical path of movement. A spline connection 127 is provided between the cutter blade and the adjacent wall of the seal magazine 32 and further assists inthe guiding function.

As best seen in FIGS. 6 and 7, the head portion 104 of the ram 100 is formed with a tangentially extending notch 130 in its outer surface, this notch being designed for cooperation with a cam latch 132 in the form of a rock shaft which is mounted in the jaw support 114. The latch 132 is recessed medially of its ends as shown at 134, thus providing an edge 136 which is engageable in the notch 130 under the influence of a biasing spring 138 (FIG. 1) in order to latch the jaw support 114 and ram 100 together for movement in unison. One end 140 cam latch 132 projects outwardly of the jaw support 114 and has a flattened surface 142 designed for engagement with a lug 144 secured to a portion of the main casting, such engagement taking place as the cutter plate and jaw support 114 move downwardly in unison. At such time as the cam latch engages the lug, further downward movement of the jaw support 114 is prevented but the angular turning movement of the cam latch 132 incident to such engagement shifts the edge 136 of the latch out of the notch 130 in the ram 100, thus freeing the ram for further downward movement. As will become clear presently, during downward movement of the jaw support 114 and prior to the time the cam latch 132 and lug 144 become engaged, the support 114 and cutter blade 66 move in unison and no relative jaw movement takes place, the two jaws serving merely to hold a seal S therebetween. After latch and lug engagement has taken place so as to release the ram for further downward movement, an initial downward displacement of the ram relative to the jaw support 114 serves to effect a rapid jaw-closing movement but only to such extent that the seal flanges become wrapped around the side edges of the strapping. Thereafter, continued downward movement of the ram relative to the support serves to effect the terminalnotching portion of the crimping cycle whereby the strapping is compressed tightly between the seal flanges and the crown portion of the seal and the various laminae thus established are notched substantially in the manner set forth in the aforementioned U.S. Pat. to Ericsson, No. 3,l98,2 l 8.

Referring again to FIGS. 3, 4 and 5, the aforementioned jaw linkage assembly 119 constitutes the principal feature of the present invention and it includes a pair of spreader links 150 for operating a pair of composite jaw members 152, each member being comprised of a plurality of individual spacedapart identical jaw sections disposed in parallelism and maintained in their spaced relationship by one or more interposed notcher bars 154. Additional notcher bars 154 lie outside the lateral confines of the jaw members as shown in FIG. 7 and the various interpositioned jaw sections and notcher bars 154 substantially bridge the distance between the cutter blade 66 and the depending side plate 120 of the jaw support 114. It is within the purview of the present invention to vary the number of jaw sections and notcher bars, a greater or lesser number of either being contemplated. However, in the illustrated form of the invention, and as best seen in FIG. 7, each composite jaw member 152 is comprised of two jaw sections with two contiguous notcher bars being interposed between these jaw sections and with one notcher bar lying in contiguous relationship on the outer side of each jaw section. It will be understood that by varying the number and disposition of the notcher bars and jaw sections, various seal notching characteristics or patterns may be attained.

Each composite jaw member 152 is mounted for swinging movement about a horizontal axis by a fixed pivot pin 156 which has its ends secured in the cutter blade 66 and side plate respectively. The notcher bars 154 are identical and each bar has its outer end regions pivotally secured to the opposed composite jaw members by means of free-floating pins 158 which project through the notcher bars 154 and jaw members 156. Clearance slots 160 are formed in the notcher bars 154 for reception of the pivot pins 156 therethrough. The lower end regions of the jaw members 152 constitute jaws proper 162 which are movable toward and away from each other as the jaw members are swung in opposite directions. Small notches 164 are formed in the jaws 162 and facilitate holding of the seals S as they are successively fed from the magazine 32 as heretofore described. It will be observed that as the jaws 162 move inwardly toward each other during any given sealcrimping operation, the free-floating pins 158 have a large component of downward movement so that they carry the various notcher bars 154 downwardly with respect to the jaw support 114. The horizontal component of movement of the pins 158 is extremely small since it depends upon the cosine of the angle involved and therefore there will be no binding of the pins and consequent obstruction to free closing movements of the jaws 162 since the lateral movement of the pins 158 is well within machining tolerances.

The upper end regions of the composite jaw members 152 are connected to the lower ends of the spreader links by means of pin and slot connections including pins 166 which pass through the various jaw sections and extend through slots 168 in the outer or distal ends of the spreader links 150, the adjacent or proximate ends of the links being pivoted to the thrust pin 118. The spreader links 150 extend between the two jaw sections and the width thereof is approximately twice the width of a notcher bar 154 to accommodate the dual thickness of metal afforded by the two medial notcher bars. The outer ends of the spreader links lie in a common vertical plane but the inner ends thereof are offset in opposite directions to facilitate their pivotal connections to the thrust pin 118.

It will be understood that in the operation of the present sealing mechanism, when the piston 106 is at the top of its stroke, the ram 100 will be maintained in the elevated position in which it is shown in FIG. 3 so that the toggle joint is completely collapsed and serves to maintain the jaw members in their positions of maximum angularity wherein there is an interfacial edge-to-edge contact between the side edges of the lower portions of the spreader links 150 as indicated at 170. The jaws proper 162 are thus maintained in their positions of maximum jaw opening which is just wide enough to admit a seal S therebetween as previously described. As the ram 100 commences its downward movement, jaw support 114, together with the entire linkage assembly carried thereby is lowered bodily as a unit to carry the seal S downwardly into a saddlelike position of seating engagement on the overlapping portions of the strap. During this downward movement, the cutter blade 66 cooperates with the cutter block 72 to shear the upper portion of the strap rearwardly of the region where the seal is immediately thereafter applied. The downward movement of the jaw support 114 continues until such time as the cam rod 132 engages the lug 144 and thus arrests further downward movement of the jaw support and cutter blade while releasing the ram 100 for further downward movement as previously described.

As the ram continues its downward movement. the sealcrimping operation is initiated by inward closing movement of the jaws proper 162. For proper jaw movement in accordance with the principles of the invention, the axes of the two slots 168 extend substantially transversely of the longitudinal axes of their respective spreader links. The downwardly and outwardly facing straight edges of these slots 168 function as cam surfaces during the initial downward movement of the ram and they exert a downward and outward component of spreading action on the associated pins 166, this spreading action serving to rapidly swing the jaw members 152 in opposite directions so as to move the jaws proper 162 inwardly toward each other and effect the preliminary wrapping of the seal flanges around the overlapping portions of the strap as shown in FIG. 4. The reaction force for this outward cam-initiated spreading action is provided by the opposed contacting edges 170 of the two spreader links 150. At such point in the sealcrimping cycle as the seal becomes deformed to the extent that the edges of the strap are engaged by the seal flanges and encompassed to the extent illustrated in FIG. 4, the jaw members 152 will have moved to positions wherein the pins 166 are disposed in the upper end regions of the slots 168, the pins 166 having been subjected to a camming action by the inside edges of the transverse slots 168 and having been shifted from the inner ends of such slots to the outer ends thereof. At this point in the crimping cycle, the wrapping portion of the cycle may be regarded as having terminated and the notching portion of the cycle as commencing.

At such time as the pins 166 have completely traversed the slots 168 in the spreader links 150, a true toggle action then takes place and continues throughout the remainder of the crimping cycle while the jaws proper 162 move inwardly toward each other and effect the notching operation. The effectiveness of this notching operation is enhanced by reason of the fact that the free-floating pins 158 which, in effect, carry the notcher bars 154 assume eccentric positions with respect to the pivot pins 156 which cause them to have a large component of downward movement as the jaws 162 complete their final inward movements. This downward movement of the pins 158 is translated to the notcher bars 154 which are provided with inclined deflector edges 172 which bear downwardly on the crown portion of the now substantially flattened seal while at the same time inclined deflector edges 174 on the intervening jaw sections bear upwardly on the seal flanges, thus effecting a multiple shearing action along the seal edges and creating the notched seal joint of FIG. 3 in a manner similar to that shown and described in the aforementioned US. Pat. to Ericsson, No. 3,198,218.

It is to be noted at this point that the vectorial thrust exerted on the pins 166 by the edges of the slots 168 for initial jawclosing movements as shown in FIG. 3 is a downward and outward thrust which tends to place the links 150 under compression and spread these pins apart. The cam angle involved is a slanting one with respect to the arcuate direction of swinging movement of the upper ends of the jaw members 152. As a consequence, the spreading action which is exerted on the pins 166 is a rapid one and it takes place at the moment that the ram commences its descent relative to the jaw support 114. The directional thrust exerted on the pins 116 is at an angle to the path of movement of these pins so that during translation of motion from the edges of the slots 168 to the .pins 116, rapid pin displacement is effected at the expense of the loss of some power. However, during this initial descent of the ram, the jaws 162 are functioning only to bend the seal flanges inwardly toward each other as shown in FIG. 4 so that a high degree of jaw pressure is not required as is the case during the final seal-notching operation. During progressive descent of the ram, the angularity of the slots 168 gradually shifts so that the directional thrust exerted on the pins 116 gradually approaches the direction of their path of movement, while at the same time the magnitude of this thrust becomes progressively greater. Thus, as the jaws 162 closely approach each other during the final notching operation, the longitudinal axis of the slots 168 move into parallelism as shown in FIG. 5 and the vectorial thrust on the pins 116 is more nearly directly in line with their path of movement of so that the full been fully crimped and notched, at no time is there any lost seal-crimping motion between the 'spreader links 150 and the I jaw members 152. There is a gradual increase of jaw pressure on the seal due to the change of inclination of the slots 168 and their consequent transmission of power to the pins 166 but there is no interruption of power application to the latter.

Return of the seal crimping jaws l62to their initial positions incident to upward movement of tli'elpiston 106 and its at- 7..

tached ram is effected by an initial 'p'artial collapse of the toggle joint, i.e. the elbow joints established by the spreader links 150 and upper portions of the jaw members 152, after which the thrust pin 118, now acting in the manner of a lift pin, completes the collapsing operation while the free-floating I pins 166 exert a camming action on the upper edges of the slots 168 and force the jaw members 152 to rotate in'opposite I directions so as to withdraw the jaws proper 162 from the notched edges of the completely crimped seal S. At such time as the jaws 162 assume their positions of maximum jaw spread, the cam rod 132 engages the notch and picks up the jaw support 114, so to speak, and carries the same upwardly to restore the cutter blade 66 to its raised position and otherwise restore the toggle linkage to its normal inoperative position as shown in FIG. 1. The tool is then in condition for the next succeeding strapping operation with the sealing mechanism 30 poised for reception of a fresh seal between the jaws 162 thereof. I

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construcas solid single-piece jaw members may be substituted therefor.

It also is within the scope of the present invention to reverse the character of the pin and slot connection between the lower ends of the spreader links and upper ends of the jaw members 152 by providing the slots 168 in the jaw members for camming cooperation .with pins which are carried by the spreader links. Finally, it is not essential that the jaw-actuating linkage mechanism of the present sealing unit be associated with a cutter blade inasmuch as in a small hand tool for example the jaw support 114 may be a fixed member within which there is mounted a vertically shiftable jaw actuator the movements of which are controlled by a manually operable operating lever. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

I claim:

1. In a strapping tool, in combination, a seal-crimping unit of the opposed jaw type for crimping an open flange type of seal having a crown portion with depending side flanges about the overlapping portions of a tensioned loop of strapping, said unit comprising a jaw support, a ram reciprocable vertically in said jaw support, a pair of divergent spreader link members having their upper ends pivoted for swinging movement of the link members in opposite directions to the ram, opposed sealengaging jaws on the lower ends of said jaw members and movable toward and away from each other between closed and open positions. the lower ends of said spreader links making Contact with each other in the open position of the jaws to limit the extent of opening movement of the latter, said jaws,

during closing movements thereof, being initially engageable with the seal flanges to effect progressive inward swinging movement and consequent wrapping thereof around said overlapping portions and subsequently to force said seal flanges in an upward direction against said overlapping portions of the loop and compress such portions between the flanges and the crown portion, means establishing a pin-andslot connection between the upper end of each jaw member and the lower end of a respective spreader link member, each pin-and-slot connection comprising a pin fixedly disposed on one member and projecting into an elongated slot in the other member and which in the fully open position of said jaws, extends at an acute angle relative to the common horizontal plane of said pins extends-substantially transversely of such member whereby, upon descent of the ram, said pins and the edges of the associated slotswill make sliding camming engagement with each other and with a progressively increasing effective cam angle to place said other members under compression and effect a positive spreading action on the upper ends of the jaw members, thus rocking the latter in opposite directions to effect closing movement of the jaws, and means for moving said ram.

2. In a strapping tool, the combination set forth in claim 1, wherein the pin of each pin and slot connection is disposed on the upper end of a jaw member while the slot of such connection is formed in the lower end region of a spreader link member. 

